1. Field of the Invention
The present invention relates to a technique for controlling a light-emission luminance of an image to be displayed on a display device such as a plasma display.
2. Description of the Related Art
A plasma display has a plurality of discharge cells arranged in a matrix form, and emits light through production of gas discharges in selected discharge cells to generate ultraviolet rays which excite fluorescent materials within the selected discharge cells. An image can be displayed at luminance levels or gradation levels of halftone by controlling the number of occurrences of the discharge per unit time in the discharge cells, i.e., the number of times a discharge sustain pulse is supplied to the discharge cells. According to a sub-field method commonly used for driving a plasma display, one field corresponding to one image is divided into a plurality of sub-fields, and ratios of sustain periods for light emission in the respective sub-fields are set to a power of two. Various combinations of the sub-fields make grayscale display. For example, when ratios of sustain periods for light emission in eight sub-fields are set to 20:21:22:23:24:25:26:27, i.e., 1:2:4:8:16:32:64:128, 256 gradation levels can be implemented by combining the sub-fields. Techniques related to the sub-field method are disclosed, for example, in Japanese Patent Kokai No. 2004-4606.
An existing plasma display has an ABL (Automatically Brightness Limit) function which variably sets the number of discharge sustain pulses in each sub-field in accordance with an average peak level (APL) of an input image signal in order to mainly reduce power consumption. The plasma display having the ABL function stores a characteristic curve indicative of the relationship of the number of discharge sustain pulses to an average peak level in a memory, and determines the number of discharge sustain pulses in accordance with a detected average peak level with reference to this characteristic curve. With this ABL function, the plasma display can reduce brightness or luminance over an entire screen by reducing the number of discharge sustain pulses in each sub-field when a high average peak level is detected, and increases brightness or luminance over the entire screen by increasing the number of discharge sustain pulses in each sub-field when a low average peak level is detected. For example, Japanese Patent Kokai No. 2003-29698 discloses an ABL function for a plasma display. The plasma display described in Japanese Patent Kokai No. 2003-29698 stores a plurality of kinds of characteristic curves, for example, a characteristic curve for standard use, a characteristic curve for burn-in prevention, a characteristic curve for power saving, and the like in a memory. A user can arbitrarily select a curve from among these characteristic curves, depending on the situation.
As described above, the ABL function mainly aims at power saving for the plasma display, but even if the ABL function is performed using the characteristic curve for power saving, the user cannot realize an actual amount of power consumption, and has no awareness of actively selecting the characteristic curve for power consumption. Also, even the characteristic curve for power saving is selected, the plasma display is not always operating with a small amount of power consumption as expected by the user.